The present invention relates to an analyzer for analyzing biomaterial such as blood or urine, particularly to an automatic analyzer equipped with a function of pipeting liquid from one container to another container by means of a pipetting probe.
To analyze the component of a sample containing biomaterial such as blood or urine, reagent is mixed in the sample and the color of the reaction liquid is measured by a measuring means such as a photometer. There has been available an automatic analyzer automating all these analysis processes, including pouring (pipeting) the sample from a sample container into a reaction container on a reaction line, mixing the reagent, measuring a mixture of the sample and reagent by a photometer, and outputting the analysis result.
To pipet the sample, the tip of a pipetting probe is dipped into the liquid for pipetting inside a sample container and the liquid is sucked by a pump or similar means, and then the sucked liquid is discharged into a reaction container. In this process, if the dipping depth of the probe into the liquid is greater, the amount of liquid adhering to the outside wall of the probe increases. The liquid adhering on the outside wall of the probe, which may be mixed into another sample to be analyzed next in the course of pipeting the sample, can be a cause of increasing so-called contamination. In order to reduce the dipping depth of the tip of the pipetting probe into the sample liquid as much as possible, the motion of the pipetting probe is so controlled that the liquid surface of the liquid inside the container is detected, the descending motion of the probe is stopped when the tip of the probe reaches a position slightly below the liquid surface, and then a specified amount of the liquid is sucked into the probe.
Known methods of detecting the liquid surface include a method by means of detecting a change in the capacitance or resistance of the sample, a method by means of detecting a change in the refraction or reflection of light or ultrasonic wave, and a method by means of detecting a change in the pressure inside the pipetting probe. Brief steps of measuring the liquid surface by a change in the capacitance are as follows. The pipetting probes and sample containers, or sample holders, are made of conductive material and the capacitance through the sample is measured. First, the capacitance at the upper dead point of the probe is registered in memory as a reference. Then, an increase in the capacitance at the time when the pipetting probe descends and contacts the liquid surface is detected and the liquid surface is judged to be detected, using the increase in the capacitance as a trigger. Disclosed in U.S. Pat. No. 5,049,826 is a prior art using the afore-mentioned upper dead point as a reference.